1. Field
The disclosure relates to pile anchor systems and methods, and particularly to pile anchor systems and methods for offshore petroleum structures, such as floating structures, drilling or production risers, and other marine structures.
2. Description of related art
Often marine structures used in offshore petroleum industry are moored to a pile that is anchored to a sea floor. The pile is generally a tubular element that is installed into seabed deposits that form the sea floor. Depending on the depth of the sea at a given location, various methods can be used to install the pile into the sea floor. At great depths, it may be problematic to use a pile-driving hammer or other equipment to install the pile.
A type of pile, known as a suction pile, is particularly suitable for deep water development. Generally, a suction pile is a tubular element with a closed top and open bottom that is installed vertically into the sea floor by self weight penetration and suction pressure. FIG. 1 is a cross-sectional schematic diagram of a pile installed into a sea floor. The suction pile, pile 2, may be installed in the sea floor 4. The pile 2 includes a top 6, sometimes known as a “pile cap,” attached to tubular sides 8, and is open at the bottom 10. The top 6 can include a valve 12 that gives access to the interior volume 11 of the pile 2 between the sides 8 and the top 6. The pile 2 further includes a padeye 14. The padeye 14 generally is a reinforced section used to attach an anchor line or other coupling member 16 to a structure (not shown) that may need mooring or otherwise securing. The installation technique generally includes locating the pile 2 in an appropriate location and lowering the pile into the sea floor 4 with cables. Typical the pile will penetrate under its own weight into the seafloor deposits until the resistance from the seabed deposits equals the self weight. Water can then be pumped out of the pile through the value 12 to create a differential pressure in the volume 11 with a net downward force to push the pile to a desired depth of full penetration.
The pile 2 can have different configurations. Some piles may include external fins that extend outwardly from the side. Other piles can include internal baffles or stiffening members that, for example, can be selectively depressurized to position the piles at different angles relative to the sea floor. Some designs have hemispherical tops. Other piles include groups of suction piles coupled together to form an assembly.
A suction pile, driven pile or any other tubular structure penetrated into the seabed to support or resist loads is referred to generally herein as a pile.
Piles can become damaged, worn, or otherwise degraded. Presently, when such piles degraded, the pile is either removed, or abandoned, and another pile is installed at another location near the first pile. In general it is considered that after the initial installation of a pile, the sea floor 4 has been disturbed and the shear resistance around the installed pile may be significantly reduced. Typically, the sea floor deposits 4 may require several months of consolidation and recovery after a pile is installed to provide full strength to the anchoring of the pile in the sea floor deposits.
Further, there are times in which an existing pile may be in a satisfactory condition, but may require to resist additional structural loads from a new design load case or change in design. These new design load cases may overstress or be beyond the capacity of the existing pile. Typically, the solution has therefore been to install an additional pile to provide further support or replace the existing pile. However, the new solution still has the disadvantage of not providing full support until some later time, when the disturbed layers on the sea floor 4 can consolidate around the pile.
Therefore, there remains a need to provide additional support to a pile either in a degraded condition or to provide additional support to extend the capacity of the existing pile.